WO2003000538A1

WO2003000538A1 - Control system for a powered trailer

Info

Publication number: WO2003000538A1
Application number: PCT/AU2002/000812
Authority: WO
Inventors: Kerren Joseph Smith
Original assignee: Smith Resources International Pty Ltd
Priority date: 2001-06-21
Filing date: 2002-06-21
Publication date: 2003-01-03
Also published as: AUPR586101A0

Abstract

A sensing assembly (20) for use in a control system for a combination vehicle of the type comprising a prime mover and at least one powered trailer, the sensing assembly (20) having first and second members at least partially rotatable relative to each other about a common axis, the first member being adapted to be connected, in use, to the prime mover and be fixed rotationally relative thereto about the axis, the second member being adapted to be connected, in use, to the trailer so as to be fixed rotationally relative thereto about the axis, load sensing apparatus mounted on the first or second member for detecting the magnitude of a force acting on the member, and direction sensing apparatus for detecting the relative orientation of the first and second members.

Description

CONTROL SYSTEM FOR A POWERED TRAILER

This invention relates to combination vehicles of the type having a prime mover and one or more trailers, at least one of the trailers being powered by an auxiliary motor. In particular, the invention is directed to a control system for a powered trailer, and a force vector sensor for use in the control system.

BACKGROUND ART Throughout this specification, the term "combination vehicle" is intended to mean a vehicle comprising a combination of a prime mover and one or more trailers adapted to be towed by the prime mover, at least one of the trailers being powered by an auxiliary motor.

Many open cut mines are now being excavated at considerable distances from processing plants or stockpile areas. The coal or ore being mined must be carried out of the mine pit, often from the bottom of the mine pit, and then transported to the processing or stockpile location, over surfaced or unsurfaced roads. Large low-geared trucks are commonly used to carry the coal or ore from the bottom of the pit to the surface. As these large trucks are designed for low speed, short haul operations, they are unsuitable for travelling long distances to a processing or stockpile area. Moreover, due to the high cost of such trucks, it would be uneconomical to use them for long haul surface transport.

Accordingly, the coal or ore is dumped by the trucks at the surface of the mine, and reloaded into bin trailers to be towed by prime movers. More than one trailer may be towed by a prime mover, depending on the power of the prime mover. Such reloading of the coal or ore into the trailers increases the time and cost of delivering the coal or ore from the mine pit to the desired processing or stockpile destination.

The trailers cannot normally be loaded directly in the mine pit itself, as the prime movers are generally incapable of pulling laden trailers up the relatively steep, and often rough-surfaced and/or loose-surfaced, inclines leading out of the pit. Combination vehicles having self-powered trailers are known.

The auxiliary motor of a powered trailer provides additional driving force to the trailer wheels, enabling the vehicle to transport heavier loads. The auxiliary motor on the trailer must be operated so that the additional power is provided as and when required.

Australian patent application 77124/91 discloses a combination vehicle in which the motor on the trailer is operated from the prime mover motor via a cable, so that the output of the two motors is synchronised. That is, both motors are operated simultaneously. This leads to an inefficient arrangement, as the additional power provided by the trailer motor is not always required.

Australian patent application 200172039 also discloses a combination vehicle in which synchronisation of the power output of the prime mover and powered trailer is achieved by dual control by a single operator, using a common accelerator. This not only places additional demands on the operator, but also is inefficient as the prime mover engine will suffice for most of the time and the auxiliary engine need only be operated at times of peak demand. It is therefore desirable to have a control system which automatically employs the auxiliary engine only as and when required. Known automatic control systems generally rely on simple forms of feedback for control purposes. For example, the control systems described in U.S. patents nos. 3578096, 4502557 and 4771838 use mechanical devices to detect the relative position and/or motion between the prime mover and a trailer, and the output of the mechanical device is used to control the movement of the trailer. Such simple mechanical devices are unable to provide accurate control of heavy duty trailers.

It is also known to control the operation of a powered trailer in response to the magnitude of the force acting on the coupling between the prime mover and the trailer. International patent application WO86/04310 and Australian patent application 199954000 describe control systems in which a load cell senses the force acting on the coupling, and the trailer is controlled in response to the output of the load cell. However, control systems which are based solely on the magnitude of the force acting on the coupling may result in jack-knifing of the prime mover and trailer combination as the control system does not take angular displacement into account, e.g. when the vehicle combination is turning. U.S. patent 4119166 discloses a dual car operating system which permits simultaneous operation of two automobiles. The system uses a connecting link which measures the force which one car applies to the other via the connecting link, as well as angular displacement of the two cars. The sensed angular displacement is used for steering the trailing car. U.S. patent 4566553 discloses an agricultural work vehicle having a slave vehicle hinged side-by-side to it. Operation of the slave vehicle is controlled in response to the output of strain gauge sensors at the hinges between the two vehicles.

U.S. patent no. 4505347 discloses a heavy duty vehicle system having wire strain gauges arranged on a towing bar between the prime mover and a trailer to detect the force acting on the towing bar. The '347 patent suggests that a further transducer device can be provided to supply a signal depending on the angle between the towing bar and longitudinal axis of the trailer, in order to drive the wheels on the outer curve with a different speed to the wheels on the inner curve during travel along a curve. However, the '347 patent does not disclose how the wheels are to be controlled, nor does the '347 patent teach if or how the output of the auxiliary motor is changed in response to the angle transducer.

U.S. patent 5330020 discloses a mechanical arrangement using push/pull cables between the towing vehicle and a self-powered trailer to detect relative angular displacement between the towing vehicle and the trailer and to apply power differentially to the wheels. Such push/pull cables are unsuitable for heavy duty combination vehicles.

The known control systems are not considered to be applicable or suitable for providing safe controlled driving forces to trailer wheels of heavy duty combination vehicles, particularly in mine pit conditions. For example, known control systems may not be suitable for use on the curved inclines in mine pits where the prime mover may be angled to the trailer and/or on rough surfaced inclines where wheel slip may occur.

It is a general object of this invention to provide an improved control system for a combination vehicle. It is a particular object of this invention to provide a sensing assembly for use in the control system, for detecting a towing force vector.

SUMMARY OF THE INVENTION In one broad form, the invention provides a sensing assembly for use in a control system for a combination vehicle of the type comprising a prime mover and at least one powered trailer, the sensing assembly having first and second members at least partially rotatable relative to each other about a common axis, the first member being adapted to be connected, in use, to the prime mover and be fixed rotationally relative thereto about the axis, the second member being adapted to be connected, in use, to the trailer so as to be fixed rotationally relative thereto about the axis, load sensing apparatus mounted on the first or second member for detecting the magnitude of a force acting on the member, and direction sensing apparatus for detecting the relative orientation of the first and second members.

Typically, the first and second members form a heavy duty bearing which serves as a rotatable coupling between the prime mover and the trailer. The second member is an annular member, and the first member is a circular plate member located within the annular member and substantially co-planar therewith. The plate member is able to rotate relative to the annular member about their common axis.

In the preferred embodiment, a king pin is mounted to the underside of the first member, for removable connection to the prime mover. A locking member prevents relative rotation of the king pin and first member relative to the prime mover

The load sensing apparatus may suitably comprise two strain gauges mounted on the plate member along a diameter thereof aligned with the direction of pull of the prime mover. Increased accuracy from the strain gauges is obtained as they are always aligned with the direction of pull of the prime mover.

The direction sensing apparatus suitably comprises a bar magnet mounted to the plate member, and an adjacent magnetic field sensor fixed relative to the annular member. The magnetic field sensor has an output dependent on the orientation of the bar magnet relative thereto. The sensor output is therefore dependent on the relative orientation of the first and second members, and hence the prime mover and trailer. In another form, the invention provides a control system for a combination vehicle, the control system including a sensing assembly as described above.

Typically, the control system includes a control valve for varying the application of hydraulic power to the driven wheels of the trailer, the control valve being operatively controlled by an electronic controller of the control system. The electronic controller is programmed to control the control valve in response to the outputs of the load sensing apparatus and the direction sensing apparatus of the sensing assembly located at the coupling of the prime mover to the trailer. These outputs represent the magnitude of the tow force at the coupling of the prime mover and the trailer, and the angle of that force.

In the preferred embodiment, the trailer has both driven and non-driven wheels, and the control system also includes speed sensing apparatus for sensing the rotational speeds of the driven and non-driven wheels. The electronic controller is programmable to control the control valve in response to differences in the rotational speeds of the driven wheels and the non-driven wheels, indicative of wheel spin or loss of traction.

Typically, the electronic controller is located on the trailer, but the control system may include a display and an operator-controlled input located in the prime mover which communicates with the electronic controller.

In another form, the invention provides a method of controlling a combination vehicle of the type comprising a prime mover and at least one powered trailer having a power plant controlled by an electronic control system, the power plant driving a set of driven wheels on the trailer, the method comprising the steps of using a sensing assembly located at the coupling of the prime mover and the trailer to detect the magnitude and direction of the force between the trailer and the prime mover, and automatically controlling the operation of the power plant in response to the measured magnitude and direction of the force.

Preferably, the method includes the further step of using speed sensing apparatus to detect the rotational speeds of driven and non-driven wheels of the trailer, and controlling the application of power by the power plant to the driven wheels of the trailer in response to the difference between the rotational speeds of the driven and non-driven wheels.

In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic elevation of a combination vehicle according to one embodiment of the invention.

Fig. 2 is an elevation of the combination vehicle of Fig. 1. Fig. 3 is a schematic block diagram of the control system of the combination vehicle.

Fig. 4A is a schematic circuit diagram of the control system of the combination vehicle.

Fig 4B is a table of inputs and outputs for the circuit diagram of Fig. 4A.

Fig. 5 is a sectional elevation of a tow force sensing assembly used in the control system of Fig. 3. Fig. 6 is a plan view of the assembly of Fig. 5.

Fig. 7 is a vector diagram illustrating the forces acting on sensing assembly of Fig. 5. DESCRIPTION OF PREFERRED EMBODIMENT As shown in Figs. 1 and 2, a combination vehicle 10 comprises a driving vehicle, such as a prime mover 11 , adapted to pull a pair of driven vehicles, such as linked trailers 12, 13. Trailer 12 has a set of driven wheels 15 mounted on an axle, and a pair of non-driven wheels 17 mounted on a lazy axle. The trailer 12 is also provided with an auxiliary motor 14 which is used to power hydraulically the drive wheels 15 of the trailer.

The auxiliary motor 14 suitably comprises an internal combustion engine which is independently governed to run at constant speed in its optimum power band. The engine drives a variable displacement hydraulic pump (not shown). The engine/pump combination provides hydraulic power to a hydraulic motor (not shown) which drives a heavy duty planetary differential through a sprag clutch on the lead axle of the trailer, i.e. the axle of the driven wheels 15. A hydraulic pump servo control valve 18 is provided on the variable displacement pump, and controls the oil flow in the closed loop hydraulic system comprising the pump and hydraulic motor.

The hydraulic drive to the axle of the driven wheels 15 is controlled by a control system, shown schematically in Fig. 3, and in more detail in the circuit diagram of Fig. 4A (read in conjunction with the table of

Fig 4B). The illustrated circuit is designed for use with a Caterpillar (CAT) engine in the auxiliary motor, but any suitable engine will suffice.

As shown in Fig 3, the control system includes an electronic controller 19, which may be an embedded controller with digital computer running software 40. A suitable embedded controller is the Tiger controller made by Wilke Technology GmbH of Germany. The electronic controller 19 receives signals from a tow force sensing assembly 20 mounted on the king pin headstock of the trailer.

The sensing assembly 20 is shown in more detail in Figs. 5 and 6. The illustrated sensing assembly 20 is designed to measure the tow force vector, i.e. the magnitude of the force acting on the coupling between the prime mover 11 and the trailer 12, and the direction of the tow force. As shown in Figs 5 and 6, the sensing assembly 20 is mounted to a skid plate 21 on the underside of the leading end of the trailer 12. The sensing assembly has a heavy duty bearing comprising an inner circular plate 22 which is rotatably mounted within an outer annular member 23 by means of a cross roller bearing 24. The inner circular plate 22 forms a headstock plate on which a replaceable king pin 25 is mounted, as can be seen in Fig. 5. The outer annular member typically comprises top and bottom mounting rings 23A, 23B which are held together by bolts 26 which fix the mounting rings to the skid plate 21. A grease seal 27 is suitably provided between the inner headstock plate 22 and the outer mount ring 23A. A cover plate is also fixed to the top mount ring 23A as a protective closure for the electronic sensing elements described below.

Although the roller bearing 24 permits the king pin headstock plate 22 to rotate relative to the outer annular member 23, stop blocks 29 are provided to limit the angular rotation of the king pin headstock plate. A wedge-shaped block 30 is also bolted to the underside of the headstock plate 22, and its purpose is described in more detail below.

A pair of load cells 31 A, 31 B are mounted to the upper side of the headstock plate 22. The load cells are mounted on opposite sides of the king pin, with their longitudinal axes orientated along a diameter of the headstock plate aligned with the axis of the wedge block 30, as shown more clearly in Fig. 6. The temperature-compensating load cells 31 A, 31 B are typically strain gauges, such as the strain links SLB-700 manufactured by Ranger Instruments of Brisbane, Australia. These strain gauges measure a force or load applied thereto along their longitudinal axis, by detecting micrometre deformation of the material underload. The strain links or gauges 30 are typically resistance elements who resistance varies according to deformation. A voltage is applied to the strain links, and the current passing through the strain links will vary according to the resistance of the strain link, and hence the deformation.

A permanent bar magnet 32 is embedded in the upper side of the headstock plate 22 at the centre thereof. The bar magnet 32 is aligned with a diameter of the headstock plate, preferably orthogonally to the load cells 31 A, 31 B. A magnetic field sensor circuit 33 is housed in an aluminium container 34 fixed to the underside of the cover plate 28 as shown in Fig. 5. The output of the sensor circuit 33 is a measure of the angular orientation of the bar magnet 32 relative to the sensor circuit.

In use, when the trailer 12 is coupled to the prime mover 11 , the king pin 25 locates in a conventional fifth wheel type truck turntable on the prime mover. The headstock plate 22 is rotated so that the wedge-shaped block 30 locates in a radial slot in the turntable which is aligned with the longitudinal axis of the prime mover. The wedge block 30 fixes the king pin headstock plate 22 (and king pin 25) rotationally relative to the turntable. That is, the wedge 30, king pin 25 and headstock plate 22 are rotationally locked to the prime mover. As can be seen from Fig. 6, this ensures that the strain gauges 31 A, 31 B, which mounted above and fore and aft of the king pin, are always aligned with the direction of movement of the prime mover 11 (represented by the arrow in Fig. 6).

Any tow force between the prime mover 11 and the trailer 12 will act on the king pin and its headstock plate 22. Such force will tend to deform the shape of the king pin headstock plate 22 from a circle to a slightly skewed ellipsoid, with the deformation being greater in the direction of the force than at right angles to it. Since the strain gauges 31 A, 31 B are fixed to the headstock plate 22, the force also causes micrometre deformation of the strain gauges. This physical change to the strain gauges changes their resistance. A voltage is applied to the strain gauges, and any change in resistance results in a change in the current flowing through the strain gauges. As the strain gauges are aligned with the prime mover, and hence with the tow force, they provide an accurate measurement of the tow force.

The strain gauges are read using an electrical circuit that provides an exciting voltage and the resultant current output is an analogue signal representing the magnitude of the load acting on the king pin headstock caused by the towing force of the prime mover. The load cell circuit is calibrated prior to use, e.g. to provide a positive value output when the prime mover is pulling the trailer, and a negative value output when the trailer is pushing against the prime mover.

The load cell circuit is calibrated to a predetermined king pin load, which is an upper load limit calculated on the basis of the mass of the prime mover, trailer and payload, and the maximum slope expected to be encountered in the field. The load cell circuit is calibrated to give a maximum output at that load. The load cells in the king pin sensing assembly may experience greater loads, but will not give a reading greater than the predetermined capacity of the circuit. The load cell circuit can be calibrated by applying a specific load to the king pin, e.g. with a hydraulic ram, during the calibration stage, and using a pressure gauge on the hydraulic ram to monitor the applied load. The load cell circuit is adjusted or calibrated to ensure that the maximum positive analogue output of the load cell circuit is achieved when the predetermined king pin load is applied in the towing direction, and the maximum negative analogue output is achieved when the same magnitude force is applied in the opposite direction. The load cell circuit is also adjusted to provide a zero signal when no force is applied to the king pin.

The predetermined king pin load is the force expected at the king pin in order to overcome rolling resistance of the known axle loads of the fully laden combination vehicle on the maximum slope likely to be encountered at the work site, for a selected division of power between the prime mover and the trailer motors. A typical assumption is that the prime mover and the powered trailer will provide driving power at a nominal ratio of 2:1. The bias of workload is usually towards the prime mover engine when the prime mover engine is larger than the trailer engine. This may vary with application, and is intended to ensure that smaller engines are not overworked and thereby wear out faster than the prime mover engines.

The bar magnet 32 is fixed relative to the king pin 25, and hence the prime mover. The magnetic field sensor circuit 33 however, is fixed relative to the cover plate 28 and the outer ring 23, and hence to the trailer 12. The angular orientation of the bar magnet 32 to the sensor 33 represents the angular orientation of the prime mover 11 to the trailer 12. Any relative angular displacement between the prime mover 11 and the trailer 12, e.g. during turning, will result in relative angular displacement between the bar magnet 32 and the sensor circuit 33. The output of the sensing assembly 20 therefore comprises analogue signals from the magnetic field sensor circuit 33, and the load cells 31 A, 31 B. The load cell output signals indicate the magnitude of the force acting on the king pin coupling between the trailer 12 and the prime mover 11 , while the output of the magnetic field sensor circuit indicates relative orientation of the prime mover 11 and trailer 12 and hence the direction of the tow force. These analogue signals are converted to digital signals for input to the electronic controller 19, and the tow force vector can then be determined by the electronic controller 19 from the output of the sensing assembly 20.

The electronic controller 19 also receives inputs from respective speed sensors on the driven wheels 15 and the non-driven wheels 17. The control program 40 of the electronic controller 19 utilises an algorithm containing a feedback loop from wheel speed sensors 41-44 provided on the driven and lazy axles of the trailer. Wheel speed sensors 41 , 42 measure the speed of the left hand and right hand wheels 15, respectively, on the driven axle, while wheel speed sensors 43, 44 measure the speed of the left hand and right hand wheels 17, respectively, on the lazy axle. The wheel speed sensors 41-44 may suitably be sensors of the type commonly used in anti- lock braking systems which count voltage spikes resulting from a notched wheel passing under a Hall effect magnetic sensor. The feedback loop regulates the rate of change of the electromagnetic hydraulic pump control valve 18 to ensure a smooth flow of power to the driven wheels in order to prevent excessive wheel slippage in the wet or sandy conditions often found in mine pits and roads. Differential rotation of the driven and lazy axles may signify wheel slippage. As shown in Fig. 3, in addition to inputs from the sensing assembly 20 and the wheel sensors 41-44, the electronic controller 19 of the control system receives inputs from the electronic control unit of the trailer auxiliary engine 14 and the hydraulic pump control valve 18. The input from the trailer engine ECU 14 provides operating data of the auxiliary motor. The input from the hydraulic pump valve control indicates the valve opening.

The inputs will be read at a predetermined timing to permit smooth changes and stop fluttering of the control valve 18. The computer program/algorithm 40 compares each input reading to a predetermined test value range. If it is within the allowable limits, then the data will be considered valid and the computer program will proceed to the next step. If it is outside the valid range an error count will be incremented and the value read again. Upon receipt of the next valid data the error count will be zeroed. This process will filter out any rapid oscillations that may build up in the system. If the error count exceeds a preset value, a system fault will be triggered and limp mode engaged with relevant fault signals to the driver.

The electronic controller 19 provides outputs to the electronic control unit of the trailer motor 14, as well as to a servo controller for the hydraulic pump valve 18. The electronic controller 19 also communicates with an operator control station 46 located in the prime mover 11.

The operator control station 46 may suitably comprise a touch screen display 47 in the driver's cab of the prime mover 11 , controlled by a personal data assistant (PDA) type computing device 48 which communicates with the controller 19. The PDA device 48 suitably includes a switch panel or keypad for driver control, and has its own communication and command software 50. The operator station control 46 allows the operator to arm and disarm the system for totally automatic operation. The display 47 alerts the driver to any fault condition in the system. The system may also be optionally armed automatically, e.g. by radio telemetry from a transmitter in the mine pit or by a GPS receiver 49.

The vector diagram of Fig. 7 indicates the forces acting through the sensing assembly 20 in a loaded trailer at rest facing uphill, being towed by a prime mover at an angle "e" from the longitudinal centre axis of the trailer, indicated by the line CB. The king pin sensor has rotated and the tow force acts along the centre line of the load cells, indicated by the line RT. The vector AT represents the towing force from the prime mover. The vector AR represents the reactive force of the trailer due to the sum of all frictional forces acting through the axle system and gravity.

To overcome the reactive force AR and thereby accelerate the trailer, either the towing force AT must increase through increased pull by the prime mover engine or additional tractor force must be added to the trailer from a powered axle thereof. Assuming that the prime mover engine and transmission system are already at maximum power output, the additional tractive force must be provided by the auxiliary motor on the trailer. Any additional tractor force (AF) from the trailer can only act along the trailer centre line CB. Such force will have a component (FC) acting perpendicularly to AT, and hence perpendicularly to the prime mover, which depends on the magnitude of the additional force and the angle e, namely

FC = AF tan e If the component of the additional tractor force acting perpendicularly to the prime mover is large enough, it will cause the prime mover trailer combination to jack-knife and possibly roll over.

This invention uses the measurements from the load cells and direction sensor to control the additional force applied to the powered axle of the trailer.

The additional trailer tractor force (TTF) required to neutralise part of the reactive force is calculated as follows:

TTF = (load cell circuit output/maximum load cell circuit output) x predetermined king pin load x cosine e In use, the electronic controller 19 uses the data received from the sensing assembly 20 to control the power applied by the hydraulic motor (not shown) to the drive shaft of the driven wheels 15 of the trailer 12. The electronic controller 19 provides an output signal which is converted to an analogue control signal which controls the electromechanical valve 38 controlling the oil flow in the closed loop hydraulic system mentioned above. The electronic controller 19 continuously monitors the tow force acting on the king pin, and controls the application of additional power to the drive wheels 15 of the trailer 12 in such a manner to prevent jack-knifing of the trailer and prime mover combination, by taking into account the angular orientation of the prime mover 11 and the trailer 12. In practice, the load on the king pin with vary continually. The conditioning factor "cosine e" ensures that the additional tractor force imparted to the trailer drive axle is introduced in a balanced manner in order to prevent the jack knife effect.

The electronic controller therefore controls the hydraulic drive to the driven wheels 15 so as to augment the pulling force of the prime mover 11 , yet limits the additional power in dependence on the angle e to prevent jack-knifing of the trailer and prime mover combination. For example, if the prime mover is turning sharply relative to the trailer, the maximum additional force permitted to be applied to the driven axle of the trailer will be substantially less than the additional force which can be applied when the prime mover is aligned with the trailer. Thus, when the prime mover 11 is turning, the drive to the driven wheels 15 is controlled in order to avoid excessive force being applied to the trailer which might cause jack-knifing of the trailer and prime mover combination.

The remaining factor to be taken into account before the controller 19 opens the electromechanical servo valve 18 controlling the hydraulic oil flow from the variable displacement pump to the hydraulic motor mounted on the differential of the driven trailer axle, is a feedback control loop monitoring the relative angular velocity of the driven and lazy axles of the trailer. This will overcome the problem when the driven wheel is bogged in wet or sandy conditions and additional wheel spin will dig the wheel in. Wheel spin is detected by differential rotation of the driven and lazy axles as measured by the wheel sensors. If driven axle wheel angular velocity (DAV) exceeds the lazy axle angular velocity (LAV) by a predetermined value then the power fed into the driven wheel must be proportioned by a wheel breakout function (WB). The value of WB can be efficiently calculated by a two dimensional look up table. A table is set up in computer memory at program initialisation. The values can be set by experimentation. The rows of the table indicate lazy axle wheel speed in suitable increments and the columns indicate driven axle wheel speed with a fractional coefficient less than or equal to 1 at the intersection of the rows and columns. This value will be referred as WB(DAV,LAV). The controlling program 40 now armed with quality data can set the opening of the electro-mechanical valve 18 on the variable displacement pump. The analogue signal sent to the valve is called the Pump Valve Setting (PVS). The algorithm to calculate it is as follows: lf TTF > 0, then PVS = TTF x TVB x WB₍DAV,LAV))/MOV

Otherwise

PVS = 0 (Prime Mover Braking Situation) where TVB is a predetermined tow force bias value so that some load will always be taken by the prime mover and prevent the powered trailer from constantly shunting the prime mover forward. This value can be empirically determined, depending on whether shunting is required when hauling from a dead start in boggy conditions.

MOV is the maximum open value of the pump valve in amps and is determined by the specifications of the solenoid settings of the control valve.

If the pump valve servo controller 18 cuts off power from the hydraulic motor, or if the trailer is being towed at a speed faster than the maximum rotation speed of the hydraulic motor, the sprag clutch disengages the hydraulic motor from the differential. This allows the drive shaft at the differential to overrun the low speed high talk hydraulic motor. The wheel speed sensors 41-44 indicate to the controller 19 when cruise speed has been attained, and the hydraulic power to the driven wheels 15 is cut off. The tractor force of the prime mover 11 is sufficient to maintain cruising speed, and the controller 19 sends an output signal to the electronic control unit of the trailer engine 14 to shut the engine down and thereby conserve fuel.

In a typical application, the trailer engine 14 is used to provide auxiliary power to the trailer in a controlled manner when the prime mover is pulling the loaded trailers out of a mine pit, but once the combination vehicle reaches cruising speed at the surface, the auxiliary power can be switched off. That is, once the wheel speed sensors indicate that cruise speed has been attained, the electronic controller causes the sprag clutch to disengage the hydraulic motor from the driven axle differential. The prime mover is able to maintain cruising speed under its own force, and the controller shuts down the trailer engine 14 to conserve fuel.

The above described combination vehicle has several advantages, including: • Heavily loaded trailers can be pulled up steep inclines in a safe and efficient manner using existing road transport engines, differentials, axles, wheels and tyres.

• The combination vehicle can be used on rough offroad conditions.

• The controller and auxiliary power system can be retrofitted to existing mining trailers.

• Driver intervention is not required after the system is armed.

• The system is not limited to a specific brand or model of prime mover.

• The system does not require input from the prime mover engine management system. The foregoing describes only one embodiment of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the appended claims.

For example, the invention is not limited to using closed loop hydraulic powered systems for driving the driven axle of the trailer. Other working fluids can be used, including pneumatic drive, hot gas, or directly coupled engines with automatic or semi-automatic gearboxes whose power output can be remotely varied. Further, although a pair of load cells are used for increased accuracy, the control system could be used with a single load cell. The invention is not limited to mining applications, and can be used in combination vehicles for transporting livestock or other cargo.

In another embodiment of the invention (not illustrated), the sensing assembly is designed for use with a king post on the prime mover, rather than a king pin on the trailer. The headstock plate has an opening dimensioned to receive the king post therein, and in use, is fixed rotationally relative to the king post and prime mover. The operation of this further embodiment is otherwise as described above.

The abovedescribed sensing assembly can also be modified so that it is mounted on the prime mover rather than the trailer. The outer annular member of the bearing is fixed to the prime mover, and the inner plate is rotatable within the outer annular member. The inner plate has a king post which locates in a socket on the underside of the trailer so as to be rotationally locked to the trailer. Alternatively, the inner plate may be provided with an aperture dimensioned to receive a kingpin on the underside of the trailer, and shaped to lock the plate against rotation relative to the kingpin.

The force measurement from the sensing assembly 20 can also be used to control retardation. For example, if the laden combination vehicle is travelling downhill on a mine ramp, the force exerted through the coupling by the trailer can be detected and used to control a separate braking or retardation system on the trailer.

Claims

CLAIMS:

1. A sensing assembly for use in a control system for a combination vehicle of the type comprising a prime mover and at least one powered trailer, the sensing assembly having first and second members at least partially rotatable relative to each other about a common axis, the first member being adapted to be connected, in use, to the prime mover and be fixed rotationally relative thereto about the axis, the second member being adapted to be connected, in use, to the trailer so as to be fixed rotationally relative thereto about the axis, load sensing apparatus mounted on the first or second member for detecting the magnitude of a force acting on the member, and direction sensing apparatus for detecting the relative orientation of the first and second members.

2. A sensing assembly as claimed in claim 1 , wherein the first and second members are portions of a bearing, the second member being an annular member and the first member being a circular plate member located within the annular member and substantially coplanar therewith, the plate member being rotatable relative to the annular member about the common axis.

3. A sensing assembly as claimed in claim 2, wherein the first member has a king pin mounted to its underside for connection to the prime mover, and a locking mechanism for preventing relative rotation of the first member and the prime mover about the axis.

4. A sensing assembly as claimed in claim 2, wherein the load sensing apparatus comprises two strain gauges mounted on the plate member along a diameter thereof.

5. A sensing assembly as claimed in claim 2, wherein the direction sensing apparatus comprises a bar magnet mounted to the plate member, and an adjacent magnetic field sensor fixed relative to the annular member, the magnet field sensor having an output dependent on the orientation of the bar magnet relative thereto.

6. A control system for a combination vehicle of the type comprising a prime mover and at least one powered trailer having a power plant controlled by the control system for powering a set of driven wheels of the trailer, the control system including a sensing assembly adapted to be mounted at the coupling of the trailer to the prime mover and having first and second members at least partially rotatable relative to each other about a common axis, the first member being adapted to be connected, in use, to the prime mover and be fixed rotationally relative thereto about the axis, the second member being adapted to be connected, in use, to the trailer so as to be fixed rotationally relative thereto about the axis load sensing apparatus mounted on the first or second member for detecting the magnitude of a force acting on the member, and direction sensing apparatus for detecting the relative orientation of the first and second members, and thereby the relative orientation of the prime mover and the trailer.

7. A control system as claimed in claim 6, wherein the first and second members are portions of a bearing, the second member being an annular member and the first member being a circular plate member located within the annular member and substantially coplanar therewith, the plate member being rotatable relative to the annular member about the common axis.

8. A control system as claimed in claim 7, wherein the first member has a king pin mounted to its underside for connection to the prime mover, and a locking mechanism for preventing relative rotation of the first member and the prime mover about the axis.

9. A control system as claimed in claim 7, wherein the load sensing apparatus comprises two strain gauges mounted on the plate member along a diameter thereof aligned with the direction of pull of the prime mover.

10. A control system as claimed in claim 7, wherein the direction sensing apparatus comprises a bar magnet mounted to the plate member, and an adjacent magnetic field sensor fixed relative to the annular member, the magnet field sensor having an output dependent upon the orientation of the bar magnet relative thereto.

11. A control system as claimed in claim 6, further comprising an electronic controller having a programmable computing device.

12. A control system as claimed in claim 11 , wherein the power plant drives the driven wheels hydraulically, the power plant including a control valve for varying the application of hydraulic power to the driven wheels by the power plant, the control valve being operatively controlled by the electronic controller.

13. A control system as claimed in claim 12, wherein the electronic controller is connected to outputs of the load sensing apparatus and the direction sensing apparatus of the sensing assembly, the electronic controller being programmable to control the control valve in response to said outputs.

14. A control system as claimed in claim 13, wherein the trailer also has a set of non-driven wheels, the control system further comprising speed sensing apparatus for sensing the rotational speeds of the driven and non- driven wheels, the electronic controller being connected to the outputs of the speed sensing apparatus, and programmable to control the control valve in response to differences in the rotational speeds of the driven wheels and the non-driven wheels.

15. A control system as claimed in claim 11 , wherein the electronic controller is located on the trailer, the control system further comprising a display and an operator-controlled input located in the prime mover and in communication with the electronic controller.

16. A control system as claimed in claim 11 , wherein the power plant includes an internal combustion engine operatively controlled by the electronic controller.

17. A control system as claimed in claim 16, further comprising speed sensing apparatus for detecting the rotational speed of the wheels of the trailer, the electronic controller being connected to the output of the speed sensing apparatus and programmable to control the operation of the engine in response thereto.

18. A method of controlling a combination vehicle of the type comprising a prime mover and at least one powered trailer having a power plant controlled by an electronic control system, the power plant driving a set of driven wheels on the trailer, the method comprising the steps of using a sensing assembly located at the coupling of the prime mover and the trailer to detect the magnitude and direction of the force between the trailer and the prime mover, and automatically controlling the operation of the power plant in response to the measured magnitude and direction of the force.

19. A method as claimed in claim 18, further comprising the steps of using speed sensing apparatus to detect the rotational speed of the wheels, and controlling the operation of the power plant in response to the output of the speed sensing apparatus.

20. A method as claimed in claim 18, wherein the trailer also has a set of non-driven wheels, the method further comprising the steps of using speed sensing apparatus to detect the rotational speeds of the driven and non-driven wheels, and controlling the application of power by the power plant to the driven wheels in response to the difference between the rotational speeds of the driven and non-driven wheels.